Strip material loop control



Nov. 8, 1949 w. FEW 2,487,755

STRIP MATERIAL LOOP CONTROL Filed Sept. 11, 1947 2 Sheets-Sheet 1 1 MW QM HTTOR'A/EY Nov. 8, 1949 w. FEW

STRIP MATERIAL LOOP CONTRCSL Filed Sept. 11, 1947 2 Sheets-Sheet 2 HTTOR/Vi) Patented Nov. 8, 1949 STRIP MATERIAL LOOP CONTROL William Few, Cleveland Heights, Ohio, assignor to The Clark Controller Company, Cleveland, Ohio, a corporation of Ohio Application September 11, 1947, Serial No. 773,341

18 Claims. (Cl. 318-6) This invention relates generally to strip or web material feeding apparatus of the type sometimes designated as loopers.

In apparatus of this class in general, a strip or web of material is fed at a predetermined rate to a machine or process or other point of use by a rotary or other feeding mechanism. The material is supplied to the feeding mechanism from a supply source of the material. A loop is provided in the material between the supply source and the feeding mechanism. The source material is supplied to the loop, as to a reservoir. The rate of supply may vary, and tend to vary the length of the loop and is regulated in response to variations in the length of the loop, if and as they occur, to always maintain the loop. The material may therefore be drawn from the loop reservoir and fed to the point of use at the desired rate without being interfered with by variations in the rate of supply.

In some cases, the material supply is a reel or drum on which a great length of the material has b en wound, and the reel is rotated by motor power to unwind the material and supply it to the loop, and the rotational speed of the reel dru motor is regulated.

In other cases, the material is supplied linearly from a source and is fed to the loop by a motor driven supply mechanism in the line of the supply; and the speed of the motor is regulated.

In other cases, a great length of material is fed to a reel or drum to be wound up on it. In such cases, the supply may be linear as for example from a machine or process in which the strip is manufactured; and the strip is supplied therefrom to the loop; and the winding reel is motor driven and draws the material from the loop; and the speed of the reel driving motor is regulated.

The present invention relates particularly to apparatus of this class in which the motor whose speed is regulated to maintain the loop, in any case, is an electric motor; and the primary object of the invention is to provide an improved speed regulating control for the motor, responsive in an improved manner to variations in the length of the loop. I

Other objects are:

To provide improved means to stabilize the aforesaid regulation of the motor speed.

To provide an improved speed regulating motor control as aforesaid which responds in an improved manner to variations in the illumination of photo-electric tubes efiected by variations in the length of the loop.

The invention is fully disclosed in the following description taken in connection with the accompanying drawing, in which:

Fig. 1 is a diagrammatic view illustrating a reel unwinding type of apparatus in which a strip of material is fed to a point of use from a loop which loop actuates photo-electric tubes,

and to which loop the strip is supplied from a supply reel, driven by a motor the speed of which is regulated;

Fig. 2 is a View similar to Fig. 1, but of the in the line type in which the strip is supplied to the loop linearly from a source by motor power the speed of which motor is regulated;

Fig. 3 is a diagrammatic view illustrating an electronic tube rectifying system, by which the field of the regulated motor of Fig. 1 or Fig. 2 is energized by rectified current from alternating current mains;

Fig. 4 is a diagrammatic view of a. phase shifting system for the rectifier tubes of Fig. 3, by which the field energizing output of the system of Fig. 3 is controlled by unidirectional current in a saturable reactor winding;

.Fig. 5 is a diagrammatic view illustrating a regulating system responding to the variations of photo-electric tube actuation by the loop of Fig. 1 or Fig, 2 and controlling the energization of the saturable reactor winding of Fig. 4; and illustrating certain regulation stabilizing features of the invention;

Fig. 6 is a diagrammatic view similar to Fig. 5 but illustrating modifications thereof which adapt it to the regulation of a reel winding up" type of apparatus.

Referring to the drawing, Fig. 1, there is shown at l a rotatably supported reel or drum having Wound thereon a supply 2 of strip or web material, the free end 3 of which in the unwinding direction is formed into adepending loop 4 and therebeyond is directed linearly as at 5 through a feed mechanism which (in the diagrammatic showing chosen for'illustration) comprises rolls 6-4 engaging the strip therebetween and the roll 6 being driven by a motor 8 to draw material from the loop 4 and feed it as at 9 to the point of use.

The drum I is rotably driven, through speed reduction gearing ID by a motor ll whose speed is to be regulated, to unwind the material from the reel I and supply it to the loop 4.

The motor II has a field winding l2 by which its speed is regulated, regulating energizing current being supplied thereto by mains 13-14.

The field i2 is also connected across mains I29,

at a predetermined constant potential, through an adjustable resistor I30 whereby the field strength cannot be reduced, by regulation at its mains l3-I4, below a predetermined minimum.

Preferably the armatures of the motors 8 and II are supplied with current from a common source [5, preferably at constant potential, by mains IB-l'l for the motor I! and mains i8-l9 for the motor 8 whereby if desired they may be started up or stopped in unison, by well known means not shown. The field I! of the motor 8 is preferably supplied with current at constant potential from the mains I29 by wires I32.

The loop 4 depends into a housing 20 (which may if desired also contain other parts of the apparatus to be referred to) and as will be understood its lower end 2| tends to rise or fall when the rate of supply by the reel l becomes lesser or greater respectively than the rate of feed from the loop at 9 by the motor 8.

Within the housing at one side of the loop is a vertical bank of electric lamps 22-22, and on the other side a vertical bank of closely spaced photo-electric tubes 23-23. These banks extend vertically over the whole distance, or zone of movement, through which the end 2| of the loop may rise and fall in operation. The lamps illuminate the tubes except where the light is cut off from them by the loop 4 therebetween.

By having a bank of many lamps 22-22 and having a bank of closely spaced tubes 23-23, the effect is substantially the same as that of a continuous vertical lamp (which is possible and could be substituted for the several lamps) illuminating a continuous vertical photo-electric tube, (which in the present state of the art is not practicable). The bank of photo-tubes 23-23 as will be described later (see Fig. are all connected in parallel, and current is caused to flow through them all, and the total amount of current flowing is modulated or varied by the photo-electric action of the ones of the bank that are illuminated. As a result, rise or fall of the end 2| of the loop efiects a gradual, stepless, change of current in the photo-electric tube circuit.

The end of the loop 2! may tend to rise or fall due to various causes, such for example as a change in the rate at which the strip at 5 is drawn from the loop; but it will inevitably tend to rise as it is unwound from the reel I, because of the reduction in diameter and peripheral speed of the wound supply 2.

Upon a rise of the end 2| of the loop, the field l2 of the motor I! is weakened (by the regulation to be described) to speed up the motor H and counteract the rise. If the speed-up is more than necessary to maintain the loop, the reverse action will take place and slow down the motor and lower the loop. The end 2| of the loop thus gradually rises as the reel I unwinds more and more of the supply 2; and the current in the photo-electric tube circuit gradually increases accordingly; and this increasing current in the photo-tube circuit is utilized to regulate the field I2 to weaker and weaker values; a minimum value being predetermined as heretofore described.

Referring to Fig. 3, the field I2 is reproduced, and as shown its supply mains are the output mains of an electronic tube rectifier. A transformer primary 24 connected to alternating current supply mains 25 at substantially constant potential, energizes a bi-phase secondary 26 to the mid-point of which the field main I3 is con- 4 nected; and to the ends of which are connected the anodes of tubes 21-28, whose cathodes are connected together and to the field supply main The primary 24 also energizes a secondary 29 to which are connected potential mains 30-3! for various purposes.

A. transformer primary 32 across the mains 30-3! has a bi-phase secondary 33, its secondary circuit being omitted for simplification; the secondary circuit being shown however in Fig. 4 where the primary 32 with its secondary 33 are reproduced. Across the ends of the secondary 33 in Fig. 4 is connected a loop 34 containing a resistor 35 and two inductive windings 36-31, in parallel, of a D. C. saturable reactor 38, having a direct current winding 39. A circuit 40 containing two transformer primaries ll-42 in parallel is connected between the midpoint of the secondary 33 and a point between the resistor 35 and the saturable reactor 38; and the primaries 4l-42 have respectively secondaries 43-44.

These secondaries are shown in Fig. 4 without circuits, for simplification; the circuits however being shown in Fig. 3 where the primaries 41-42 with their secondaries 43-44 are reproduced; and as shown in Fig. 3, the secondaries 43-44 are connected together at one end at 45, and their juncture connected to the common cathode line M by a wire 46. The other ends of the secondaries 43-44 are connected to the grids of the tubes 21-28 respectively.

Figs. 3 and 4 taken together will therefore be recognized by those skilled in the art as a conventional tube rectifier system (Fig. 3) having a conventional phase shift system (Fig. 4) and as supplying rectified current to the field mains I3-l4, of increasing amount when the energization of the saturable reactor winding 39 is increased and of decreased amount when energization of the winding 39 is decreased. The winding 39 is reproduced in Fig. 5 in connection with the system by which its energization is controlled.

Another transformer primary 4! across the potential mains 30-3! of Fig. 3, has a bi-phase secondary 48 shown without a circuit for simplification; the secondary circuit however being shown in Fig. 5 where the primary 4'! and secondary 48 are reproduced. The ends of the secondary 4B are connected to the anodes of a pair of rec-' tifier'tubes 49-50, the cathodes of the tubes being; connected together and to an outputmain 5| and the mid-point of the secondary 48 being con-g nected to a corresponding output main 52.

A conventional full wave rectifier is thus pro: vided for supplying rectified current to the cut put mains 51-52 and thence to control system mains 53-54, at substantially constant potential, subject to such slight variations as may incidentally occur; and the potential across the control mains 53-54 is corrected for such variations and maintained closely approximate to constant potential, by a, voltage regulating tube 55 of known type and mode of operation. The connections for this purpose are conventional as follows.

The terminals of the voltage regulating tube 55 are connected by wires 56-51 to the control mains 53-54. The rectifier output main 52 is connected directly to the control main 54. The rectifier output main 5| is connected through a. cross connection at the tube 55 shown in dotted line at 58, to a wire 59 and thence through an inductive choke winding 68 and a resistor BI to the control main 53, a capacitor 82 being connected by wires 6384 between the choke inductive winding 88 and the main 52.

The conventional voltage regulating tube 55 has a plug and Socket mounting, and the cross connection 58 is associatedtherewith, so that if the tube were removed from the socket inadvertently, the cross connection would be opened, thereby disconnecting the output potential of the rectifier mains I52 with respect to the control mains 53-54, as a safety measure.

A voltage divider shown generally at 88 is connected between the control mains 53 and 54 comprising resistors 81 to I2 inclusive. A connection point I3 between the resistors 89 and I8 will be referred to.

A regulating tube 14 is provided, comprising two cathodes 'I5-'I6 connected together and both connected through a resistor 11 to the control main 54; and having corresponding anodes I8'I9; the anode I9 being connected directly to the control main 53, and the anode 18 being connected to the control main 53 through the aforesaid direct current Winding 39 of the saturable reactor (here reproduced from Fig. 4) and through a resistor 88, across which is connected a capacitor 8I. The tube I4 has, correspondingly, two control grids 82-83.

The tube 14 is preferably a double tube having a single envelope, for the sake of greater stability as to certain internal actions to be referred to.

At 84 is a three element tube having its anode 85 connected directly to the main 53 and its cath- Ode 88 connected by a wire 81 to the main 54 through a resistor 88; and the tube has a corresponding control grid 89.

The bank of lamps 22--22 and the bank of photo-electric tubes 2323 described in connection with Fig. 1 are reproduced here in Fig. 5. The lamps 22-22 are all connected in parallel across energizing mains 98-9I in Fig. 5, reproduced from Fig. 3 where as shown they are connected to the transformer secondary 29, and the lamps are thus constantly energized.

The bank of photo-tubes 23-23 are connected in parallel between mains 92-93, the main 93 being connected to the control main 54; and the photo-tube main 92 being connected by a wire 94 through a resistor 95 by a wire 98 to a wire 9'! connected to the said voltage divider point I3; and the grid 89 of tube 84 is connected to the wire 94.

A potentiometer I88 having a movable contact IN and a resistor 99, has one end of the resistor connected to the wire 91, the other end being connected by a wire 98 to the wire 81.

The movable contact I8I is connected by a wire I82 to one end of the resistor I83 of a potentiometer I84, the movable contact I85 of which is connected to the grid 82 of the tube I4. An adjustable capacitor I88 is connected to the other end of the resistor I83 and to the upper end of the winding 39.

The grid 83 of the tube I4 is connected to the movable contact I81 of a potentiometer I88, the resistor I89 of which is connected across the terminals of a generator II8 in series with an adjustable capacitor III.

One terminal of the generator H8 is connected to the movable contact II2 of a potentiometer II3, the resistor II4 of which is connected across the voltage divider resistors 59 and I8, by wires II5-I I6.

The generator .II8 is of the type sometimes known as a tachometer generator, and is reproduced from Fig. 1, wherein it is shown as driven at a speed proportional to that of thereel I, by being geared to the gearing I8. It has a constant field produced preferably by a permanent magnet 7; but the field may be produced by field windings energized at a constant value. Its output potential is thus substantially proportional to its speed.

The cathode heating elements of the various tubes shown conventionally under their respective cathodes are heated by current from the secondary I28A (Fig. 3) of a transformer having a primary I28 connected across the potential mains 38-3I. At I28B-I28B are indicated representative ones of the heating elements, the circuits to these elements in Figs. 3 and 5 being omitted to avoid complications in the drawing.

The operation of the apparatus as above described will now be given.

In Fig. 5, potential between the point I3 on the voltage divider 66, and the control main 54, causes current to flow through the wire 91, wire 96, resistor 95, wire 94, to photo-tube main 92, through the photo-tubes 23, to main 93 and thence to control main 54.

With the reel driving motor II and the feed motor 8 of Fig. 1 both running, and assuming that the loop 4 has been formed, the end of the loop 2I will be somewhere in a vertical range of movement between the lamps 22 and photo-tubes 23, and the photo-tubes will modify the value of this said current by increasing it, in accordance with the photo-electric effect of those of the tubes that are illuminated.

This modified or increased current, which may now be referred to as the photo-tube current, produces a drop of potential in the resistor 95 through which it flows.

It will be apparent that the potential of the point I3 minus this drop of potential in the resistor 95, is impressed upon the grid 89 of the tube 84; and that a corresponding value of main current is caused to flow through the tube 84 and through the resistor 88; and determines a potential at the wire 81 and cathode 88.

With this arrangement, which will be recognized as a cathode follower arrangement, the potential at the wire 81 rises and falls with rise and fall of the current through the tube 84 caused by rise and fall of the potential at the wire 94, caused by decrease and increase respectively of photo-tube current in the resistor 95. I

The variable potential at the wire 81 is communicated to the wire 98 and to one end of the resistor 99; the constant potential of the wire 91 being communicated to the other end. The resultant potential, determined by the setting of the movable contact I8I, is communicated from the movable contact IN to the wire I82; and thence is communicated to the grid 82 of the tube I4 through a part of the resistor I83 and movable contact I85 of the potentiometer I84.

This causes the tube I4 to pass a value of current through the anode I8 and cathode I5 and through the resistor 88, saturable reactor winding 39, and resistor 11.

The energization of the saturable reactor winding 39 in this manner, (with reference to Fig. 4 as described), shifts the phase on the rectifier tubes 21-48 (Fig. 3 as described) to cause them to energize the field winding I2 of the reel motor II to a corresponding value, and the motor II drives the reel, and supplies strip to the loop 6 at a corresponding rate.

If this rate is not great enough to maintain the loop, the loop end 2| will rise, the photo-tube current will increase, the drop in the resistor 95 will increase, the potential at the wire 94 will fall, the tube 84 will pass less current through resistor 88, the potential at the wire 81 and on grid 82 will fall, tube 14 will pass less current at anode I8 and cathode l and weaken the winding 39, causing the rectifier tubes to pass less current to the motor field l2, causing the motor II to speed up and increase the rate of feed to the loop 4. If the motor I! were to go too fast, the end 2| of the loop 4 would fall, and the reverse of the above described action would occur, and the motor would slow down. As the net result, the motor is regulated by its field to run at a speed which tends to maintain a constant position for the end 2| ofthe loop.

However, for any regulated speed of the motor l the end 2| of the loop rises as the diameter and peripheral speed of the reel decrease with payingoif of the strip; and this rise concurrently causes the speed of the motor to increase by the action described aboveto halt the rise, so that the motor speed gradually increases and the loop end gradually rises, as the reel pays off strip.

There will therefore be a total range of vertical movement for the end 2| of the loop, corresponding to a given total quantity of strip unwinding from the reel I.

The loop end 2| may be placed at or near the bottom of this range, at the start of the of the loop is too fast, this range of movement will be all used up before the reel is completely unwound; and it is a feature of the invention that the rate at which the loop gradually rises can be adjusted to prevent this, and to adapt the loop to any desired or necessary rate of rise and total rise movement to correspond to the range of maximum and minimum diameters of any chosen reel as it unwinds. This is explained as follows.

As explained above, the speed of the reel motor increases in response to an increase of phototube current. An adjustment is provided which adjusts the sensitivity of. thisresponse, that is, makes the speed increase more or makes it less fora given increase of photo-tube current. This adjustment is at the potentiometer I00.

The potential of the wire 91 at the potentiometer I00 is constant. A given change of photo-tube current causes a certain change of potential at the wire 98. It is the difierence of these potentials that is impressed, (by way of movable contact IOI) on the grid 82.

By setting of the movable contact |0|, at different positions on the resistor 99, the amount of this potential difference for a given change of photo-tube current, can be adjustably changed.

When the movable contact |0| is moved over to the left end f the resistor 99, the said response is at the maximum sensitivity, and the total range of movement of the loop end 2|, will be small for a wide range of motor speed to unwind a large reel. When the contact IN is moved in the other direction, the sensitivity of response is reduced, and the range of movement of the loop end 2| is increased. The contact ||l| can thus be set to adapt the control to a particular reel unwinding job.

The following advantage results from utilizing the so-called cathode'follower arrangement above referred to.

In practice, the housing (Fig. 1) containing the lamps 22 and photo-tubes 23, must be placed in a location where it is convenient to run the loop 4 through it. It is usually desirable to install the control system proper of Fig. 5 remote therefrom. In Fig. 5 is indicated by broken line at 20 the housing and the parts which ma be conveniently contained therein or disposed close thereto. The wires98 and 54 leading to the control system when remote from the housing 20 thus constitute a pair of transmission lines of considerable length. It would be possible (hypothetically) to supply the drop of potential across the resistor 95 to these wires directly to actuate the control system. The resistor 95 in such case would then correspond to a high impedance source of potential supplying a long pair of transmission lines. It is well known that in such a case any incidental change in the current in these transmission lines, for example by current leakage therefrom, or by the picking up of alternating impulses as often occurs, will make a relatively great change in the potential of the lines, and affect the operation of the system being controlled; whereas, as is also well known, such irregularities and defects can be eliminated if the potential source feeding these lines were a low impedance source. The cathode follower arrangement provides this low impedance potential source for the transmission lines 98-54.

When the control system is in operation as described, there may be a sudden change in the length of the loop due to some cause not under control. This would make a sudden change in the photo-tube current and a sudden change in current to the saturable reactor winding 39; resulting in a tendency for the motor speed regulating action of this winding to overtravel and change the motor speed excessively. To prevent this, the resistor bridged by the capacitor 8| is provided.

All of the current in the winding 39 normally goes through the resistor 80, and the capacitor 8| V has a normal charge. This normal current in the resistor 80 produces a normal drop of potential therein, determining a normal potential at the point I I8. If the current were to decrease suddenly, the potential at the point 8 would tend to fall suddenly, but the capacitor would discharge through the resistor and partially counteract the fall of potential at the point H8 and the current in the winding 39 is thus made to decrease gradually and overtravel is avoided. A like action occurs when the current suddenly increases; some of the current then being diverted into the capacitor.

When the current in the saturable reactor winding 39 changes, the winding 39 responds to shift the rectifier tube grid phase for the purposes described. But the saturable reactor including the winding 39 has a time constant which tends to delay its response. The loop may start to rise and the photo-tube current may start to increase, and initiate a decrease of the current in the winding 39, as described. The winding 39 may start to respond to increase the motor speed to correct for the loop rise. Any delay of response of winding 39, may allow the loop to go on rising too far, and brin about a still further decrease of current in the winding 39. By the time the response of the winding 39 catches up, it may have excessively low energization, and its regulating action on the motor I I may increase its speed too much, and return the loop too far. The motor thus may have a tendency to hunt, particularly if the change of current in the winding 39 is rapid. This is corrected by the capacitor I08 and its connections. The capacitor I08 is connected to the point H8 and to the resistor I93 of the potentiometer I 00. The grid 82 has a normal potential thereon, controlled by the phototube action as described, and normal current flows in the winding 39. For normal current in the winding 39 the capacitor I06 has a normal. charge and potential, and no current flows into or out of the capacitor I08.

A rise of the loop, as described, lowers the potential on the grid 82, tending to decrease the tube current in the winding 39 and in the resistor 80 and this raises the potential at the point II8. So long as the potential at the point H8 is rising, current will flow into the capacitor and through the resistor I03. The current flowing in the resistor I03 raises the potential on the contact I05 and on the grid 82, and tends to counteract the decrease of tube current. The decrease of the tube current in the winding 39 is therefore restrained or delayed and made more gradual, so that the saturable reactor has time to respond in accordance therewith and not overtravel as referred to. The efiectiveness of this action of the capacitor I08 may be changed by moving the contact I05 to change the amount of resistance between the contact I05 and the wire I02.

A similar action but in the opposite sense occurs when the current in the winding 39 starts to increase.

By this means, the time constant of the winding 39 and saturable reactor is compensated for, and the regulation of the reel motor speed is stabilized as to its response to the action of the saturable reactor and its winding 39.

As will be referred to later, quantitatively, the strip reel I may rotate at very high peripheral speed, and supply strip to the loop at a very high rate, and the control of its speed by the motor II, must therefore respond very sensitively to changes of strip speed, otherwise-the loop would, in a very short interval of time either be drawn completely out of the housing 20, or be piled up in folds at the bottom of the housing.

At the same time, the control of the motor speed must not overtravel" because of inherent delays of motor-speed response. In this connection, there are inherent factors which delay the motor speed response to the regulation, outside of the control system; the reel load may be heavy and have great inertia; the motor armature will have mechanical inertia, and its field and also its armature will have electrical inertia.

To compensate for these factors and to render the response to the regulation sensitive, and at the same time to ofiset the effects of said response delays and prevent overtravel of the regulation, the following means is provided.

The grid 83 of the tube 14 is at all times energized, and tube current correspondingly flows through the circuit of the anode 19 and cathode 16 and through the resistor 11.

The grid 83 is energized from the voltage divider 03. The resistor II4 of the potentiometer H3 is connected by wires H5 and H6 across resistors 69 and I0 of the voltage divider, and the movable contact II2 communicates an adjusted potential from the potentiometer resistor IIA to the grid 83, by wire II9, through a part I21 of the resistor 10 I09 of the potentiometer I08, and through its movable contact I01, and by wire I25.

The tachometer generator H0 is driven (as described) at a speed proportional to that of the reel I, and, having a constant field III, delivers a corresponding potential to a local circuit comprising the wire II9, the potentiometer resistor I09, a wire I28 and the capacitor III. For a given constant speed of the generator IIO, the capacitor III becomes normally charged and no generator current flows in the local circuit II9- I25. The positive pole of the generator is connected to the wire I I9.

When the regulation as above described responds to increase or decrease the speed of the reel motor to maintain the loop, it increases or decreases the speed of the generator H0, and current then flows in the said local circuit 9- I25, temporarily, or until the capacitor III becomes charged to a new value.

This temporary local current, upon, say, an increase of generator speed, flows from the generator and from wire II9 to wire I26; and upon a decrease of generator speed flows from the capacitor and from wire I26 to wire IIS. In either case, it flows through the potentiometer resistor I09 and produces a drop of potential in that part I21 of the resistor in the line II9I25 which energizes the grid 83; and in the one case, this drop of potential increases the potential on the grid 83 and in the other case decreases it.

The said increase of speed of the generator H0 is caused by an increase of speed of the motor I I, which occurs, as described, responsive to a reduction of potential on the grid 82. Because of the arrangement of the two main electrode circuits of the tube 14, in series with the resistor 11, the common potential of the cathodes 15-18 will tend to rise and fall as the potentials of the grids 8283 tend to rise and fall.

When as above referred to, the potential of grid 82 falls and current in the winding 39 falls, and the motor II tends to increase in speed, the potential of cathode 15 falls, following the potential of grid 82. The potential of cathode 16 being connected to cathode 15, as shown, therefore also falls. The increase of motor speed, increases the speed of the generator I I0 and this tends to raise the potential of grid 83; and the potential of cathode 16, following the potential of grid 83, tends to rise and raise the potential of cathode 15. The rising of the potential of cathode 15 tends to prevent the main cathode current through the anode and cathode 18-15 from falling as much as it otherwise would, and therefore opposes the weakening of the winding 39 and the resulting speeding up of the motor I I.

The result is that as the current in the winding 39 starts to say, decrease, and responsive thereto the speed of the reel motor and of the generator IIO start to increase, the decreasing of the current in the winding 39 is opposed by action of the generator IIO and increasing of the motor speed is opposed; and the more rapidly the reel motor speed tends to increase the greater becomes the opposition to its speed increase, due to the correspondingly greater increase of speed of the generator I I0.

Itis believed to be clear that, by a similar action, when the motor II starts to decrease in speed, its decrease is similarly opposed.

By means of the adjustability of the potentiometer I08, this speed-change-opposing feature may be made more effective or less efiective as different installations or jobs require, by introducing more or less of the resistor I09 at 21 in the energizing circuit of the grid 83.

The changes of potential on the grids 82 and 83 effects little or no change in the current flowing through the resistor TI, and accordingly changes of potential drop therein are so small as not to materially affect the potential of the oathodes 15-46 and the described action thereof. For example, a fall of potential on the grid 82 and the resulting decrease of current through the anode and cathode 18-75, and the resistor T1, is accompanied by a following fall of potential at the cathodes I and I6, and (for a given potential at the grid 83) by a corresponding increase of current through the anode and cathode IS-16 and the resistor IT. The sum of currents in the resistor TI thus tends to remain constant.

As mentioned hereinbefore, the speed of the reel motor I, gradually increases as the reel unwinds the strip, starting with a full reel of large diameter and ending with a small diameter; and during this period, the end 2| of the loop gradually rises through its range of movement.

The speed-change-opposition feature therefore will have a substantially constant and practically negligible eflectiveness, during normal operation,

because the increase of reel motor speed will be uniform and very gradual, and the generator H0, due to the capacitor III, will substantially fioat in its local circuit l I9--I26.

By moving the movable contact N2 of the potentiometer I I3, the normal vertical position of the loop end 2| may be adjustably changed at any time. Moving the contact H2 in one direction or the other to a new position, while the reel motor is running at a regulated speed, changes the normal regulating potential on the grid 83, for example, increases it. This in turn and as described, decreases the current in the winding 39 and the motor speed responding thereto increases and raises the loop end 2|. This increases the photo-tube current as described and the increase of photo-tube current tends to slow down the motor. A balance is therefore reached at which the motor speed stops increasing with the end of the loop in a new higher position and thereafter the motor speed is regulated for that position. A like operation adjusts the loop end for a new lower position.

As to the system of Fig. 2, the aforesaid in the line type of control, the speed of the motor II is to be regulated to constant speed (for a constant rate of withdrawal of strip from the loop 4 by the motort). Rise (or fall) of the end 2i of the loop is here not caused by a change of rate of the supply of the strip to the loop by change of diameter of a reel, a reel being not used. In this case, rise or fall of the end 2i of the loop is caused by a change of the speed of the motor 8 or of the motor II, due to some inherent or external cause; and rise or fall of the end of the loop actuates the control system of Fig. 5, to stop the increase or decrease of the motor speed and restore it to a constant speed. Obviously, the end 2| of the loop does not continue to gradually rise. Otherwise, the arrangement of Fig. 2 and its operation, in connection with Figs. 3, 4, and 5 is the same as that described for Fig. 1.

Fig. 6 taken with Figs. 1, 3, and 4 illustrates the system, for controlling the speed of a reel to wind up a strip supplied to a loop at constant speed. Fig. 1, as above described, may be referred to as illustrating the arrangement (to avoid more drawings) if it be'considered that the strip is 12 supplied to the loop 4 at 5 by the motor 8, and withdrawn at 3 and wound up on the reel I by the motor II, the speed of the motor being regulated by its field I2 in response to rise orfall of the loop end 2I, utilizing the control system of Fig. 6.

In this case, the reel l winds up the strip, taking it from the loop 4 and the loop end 2| rises as the diameter of the wound-up strip increases.

The rising loop exposes the bank of photo-tubes 23 to more light from the lamps 22, and the system of Fig. 6 responds thereto to strengthen the field I2 and slow down the motor to maintain the loop end 2I in its regulatin range of movement.

In Fig, 6, the photo-tube main 92 is connected by wire I 2I to the point I23 on the voltage divider 66; and the photo-tube main 93 is connected by wires I28 and I22 to the point I24 on the voltage divider, the resistor 95 being in the line of the wires I28-422.

Current is thus caused to fiow through the, photo-tubes, in the same direction as in Fig. 5.

The resistor 95 is again, as in Fig. 5, connected to the grid 89 of the tube 84, and the potential variations developed at the resistor 95 by variations of photo-tube modified current, actuate the system as in Fig. 5; but here, for example, an increase of current in the resistor 95raises the potential on the grid 89 and on the grid 82 (instead of lowering it as in Fig. 5); and the current in the winding 39 is increased, and the field l2 of the reel motor I I is increased and the motor II slows down (instead of speeding up as in Fig. 5).

Otherwise, Fig. 6 is the same as Fig. 5 and the operation of the other parts thereof is the same as that of Fig. 5; and a description thereof is deemed unnecessary.

In any system of this general class in which the speed of a motor must be varied to maintain a loop responsive to a change of position of the end of the loop, there is always present the liability that the motor speed will hunt; and the certainty that such hunting will be magnified in an installation in which the reel is of great weight and inertia and the speed of the strip and rotational speed of the reel is high. The stabilizing or anti-hunting features of the present system above described are so efiective that it opens up the field of use for apparatus of this class to installations where the wound reel may weigh forty or fifty tons or higher, and the strip may travel at 2,000 feet per minute or higher, and the diameter of the reel may start at eighty inches or one hundred inches or more when full, and reduce down to twenty inches or less when pty.

With such quantitative factors, a very slight deviation in the revolutions per minute of the motor driving the reel, from the required revolutions per minute to maintain the loop, will be enough to raise or lower the end of the loop out of its photo-tube actuatin range.

The anti-hunting feature of the present system is therefore an important improvement over prior practice. As described in detail above, it comprises the generator H0 positively driven at the speed of the motor or of the reel. Having a constant field, the generator produces a, potential proportional to its speed, and may be referred to as a speed-reference-potential. Other parts of the motor-speed control system (for example in the form of Fig. 5) respond to increase the speed of the motor in response to a rise of the loop end.

. 13 This speed-reference-potential their increases, and is utilized to reduce the effectiveness of the speed increasing response of the system. The greater the tendency for the motor speed to increase, the greater is that tendency suppressed or opposed. I

This anti-hunt feature is furthermore supplemented by the above described action of the resistor 80 and condenser 8i; and of the resistor I03 and capacitor I06, which, respectively stabilize the energization of the control winding 39 to prevent sudden changes thereof, and prevent changes of energization of the winding 39 from overtravelling its controlling action.

Iclaim:

1. In connection with a power system for maintaining a loop in a longitudinal moving strip of material by means of a variable speed electric motor provided with means for propelling the I strip at one side of the loop and the motor having a variably energizable field winding for varying its speed; a control system for the motor comprising an elongated bank of parallel-connected photo-electric-tubes and a source of light, between which the loop is interposed; the tube bank being variably responsive to illumination of different portions or its length by the source upon changes of length of the loop; a photo-tube circuit including the photo-tubes, and a source of potential for causing current to flow through the phototube circuit and to be variably modified by the light response of the photo-tubes; an electronic tube having a main anode-cathode circuit and a control grid; a source of potential for the tube main circuit; a saturable reactor control winding in the main tube circuit; means including resistance in the photo-tube circuit, developing variable control potential commensurable with the variable current in the photo-tube circuit;

circuit means impressing potential on the tube grid commensurable with the control potential to vary the energization of the control winding; field mains for connection to the motor field; a full wave rectifier comprising tubes and control grids therefor, for supplying rectified current from an alternating current source to the field mains; a phase shifting system for the rectifier tube grids to vary the current supplied to the field mains, including a saturable reactor responsive to variable energization of the said control winding.

2. In connection with a power system for maintaining a loop in a longitudinall moving strip of material by means of a variable speed electric motor provided with means for propelling the strip at one side of the loop and the motor having a variably energizable field winding for varying its speed; a, control system for the motor COl'llprising an elongated bank of parallel-connected photo-electric-tubes and a source of light, between which the 100p is interposed; the tube bank being variably responsive to illuminaton of different portions of its length by the source upon changes of length of the loop; a photo-tube circuit including the photo-tubes, and a source of potential for causing current to flow through the photo-tube circuit and to be variably modified by the light response of the photo-tubes; a first electronic tube having a main anode-cathode circuit and a control grid; a saturable reactor control windin in the main tube circuit; a second electronic tube having a main anode-cathode circuit and a control grid; a source of potential for the said tube main circuits; a first resistor in the photo-tube circuit developing variable potential commensurable with the variable current in the photo-tube circuit;

l 14 connections impressing the variable potential on the grid of the second tube to vary the main current therein; a second resistor in the main circuit of the second tube connected to its cathode; a source of constant potential, and connections impressing upon the'grid of the first tube a potential commensurable with the difference between the constant potential and the potential of the cathode of the second tube; field mains for connection to the motor field; a full .wave rectifier comprising tubes and control grids therefor, for supplying rectified current from an alternating current source to the field mains; a phase shifting system for the rectifier tube grids to vary the current supplied to the field mains, including a saturable reactor responsive to variable energize.- tion of the said control winding.

3. In connection with a power system for maintaining a loop in a longitudinally moving strip of material, by means of an electric motor having a speed controlling field winding, and provided with means for propelling the strip at one side of the loop; a control system for the motor comprising: motor field energizing mains; a full wave rectifier comprising tubes and control grids therefor for supplying rectified current from an alternating current source to the field mains; a phase shifting system for the rectifier tube grids to vary the current to the motor mains, including a saturable reactor and a control winding therefor; a pair of electronic tube main electrodes having a main circuit; a source of potential for the main circuit; a control grid for controlling current in the main circuit, in response to changes of potential on the grid; the main circuit connected to the control winding to control its energization; a photo-tube and a source of light, between which the loop is interposed; a circuit for the photo-tube in which variable current fiows responsive to variable illumination of the tube effected by change of length of the loop; a source of potential and circuit means energized thereby, comprising means to impress potential on the control grid varying in response to changes of current in the photo-tube circuit.

4. In connection with a power system for maintaining a loop in a longitudinally moving strip of material by means of a variable speed electric motor provided with means for propelling the strip at one side of the loop and the motor having a variable energizable field winding for varying its speed; a control system for the motor comprising an elongated bank of parallel-connected photo-electric-tubes and a source of light, between which the loop is interposed; the tube bank being variably responsive to illumination of different portions of its length by the source upon changes of length of the loop; a photo-tube circuit including the photo-tubes, and a source of potential for causing current to flow through the photo-tube circuit and to be variably modified by the light response of the phototubes; a first electronic tube having a main anode-cathode circuit and a control grid; a saturable reactor control winding in the main tube circuit; a second electronic tube having a main anode-cathode circuit and having a control grid; a source of potential for the tube main circuits; a first resistor in the photo-tube circuit in which the variable current in the circuit develops a variable control potential; connections for energizing the second tube grid with potential commensurable with said control potential, to vary the main current in the second tube; a sec- 0ndv resistor in the main circuit of the second tube connected to its cathode; a source of constant potential; connections for energizing the grid of the first tube with potential commensurable with the difierence between the potential of the second tube cathode and the constant potential; a potentiometer for adjustably varying said potential difierence; field mains for connection to the motor field; a full wave rectifier comprising tubes and control grids therefor, for supplying rectified current from an alternating current source to the field mains; a phase shifting system for the rectifier tube grids to vary the current supplied to the field mains, including a saturable reactor responsive to variable energization of the said control winding.

5. The control system for the motor described in claim 1 and in which a decrease of phototube light response, efiects a decrease of the current in the electronic tube and a decrease of energization of the control winding, and a decrease of rectified current supplied to the field mains.

6. The control system for the motor described in claim 1 and in which an increase of phototube light response, efiects an increase of the current in the electronic tube and an increase of energization of the control winding, and an increase of rectified current supplied to the field mains. 7. In connection with a power system for maintaining a loop in a longitudinally moving strip of material, by means of an electric motor having a speed controlling field winding, and provided with means for propelling the strip at one side of the loop; a control system for the motor comprising: motor field energizing mains; a full wave rectifier comprising tubes and control grids therefor for supplying rectified current from an alternating current source to the field mains; a phase shifting system for the rectifier tube grids to vary the current to the motor mains, including a saturable reactor and a control winding therefor; a photo-tube and a source of light between which the loop is interposed; a photo-tube circuit for the photo-tube in which variable current fiows responsive to variable illumination of the tube efiected by changes of length of the loop; a pair of electronic tube main electrodes having a main circuit; a source of potential for the main circuit; a control grid for controlling current in the main circuit, in response to changes of potential on the grid; the control winding and a resistor connected in series in the tube main circuit, with the control winding between the tube and the resistor; a capacitor bridging the resistor; means including resistance in the photo-tube circuit, developing variable control potential commensurable with the variable current in the circuit; a control circuit impressing potential on the tube grid commensurable with the control potential to vary the energization of the control winding; a capacitor connected at one side to a point between the control winding and the resistor and at the other side to a resistor in said control circuit.

8. In connection with a power, system for maintaining a loop in a longitudinally moving strip of material, by means of an electric motor having a speed controlling field winding, and provided with means for propelling the strip at one side of the loop; a control system for the motor comprising: motor field energizing mains; a full wave rectifier comprising tubes and control grids therefor for supplying rectified current from an alternating current source to the field mains; a phase shifting system for the rectifier tube grids to vary the current to the motor mains, including a saturable reactor and a control winding therefor; a first electronic tube anode and cathode having a main circuit; a first control grid for controlling current in the main circuit,

in response to changes of potential on the grid; the main circuit connected to the control winding to control its energization; a photo-tube and a source of light, between which the loop is interposed; a circuit for the photo-tube in which variable current flows responsive to variable illumination of the tube eflected by changes of length of the loop; means comprising a source of potential and circuit means energized thereby, to impress potential on the first control grid varying in response to changes of current in the phototube circuit; a second electronic tube anode and cathode having a second main circuit, and a second control grid for controlling current in the second main circuit, and the second cathode connected to the first cathode; resistance means connected to the cathodes through which the current in both main circuits flows; an electric generator having a substantially constant field driven at speeds proportional to the speed of the motor; a local output circuit from one output side of the generator, through a local circuit resistor and a capacitor to the other side; a source of potential connected to said one side of the generator; connections communicating potential from said one side of the generator through the local circuit resistor to the said second control grid.

9. In a motor speed control system for a motor having a speed controlling field winding; motor field energizing mains; a full wave rectifier comprising tubes and control gridstherefor forsupplying rectified current from an alternating current source to the field mains; a phase shifting system for the rectifier tube grids to vary the current to the motor mains, including a saturable reactor and a control winding therefor; a first electronic tube anode and cathode having a main circuit; a first control grid for controlling current in the main circuit, in response to changes of potential on the grid; the main circuit connected to the control winding to control its energization; an actuating circuit; means causing actuating current to flow in the actuating circuit; means for changing the actuating current responsive to a change of motor speed; means comprising a source of potential and circuit means energized thereby to impress potential on the first control grid varying in response to changes of current in the actuating circuit; a second electronic tube anode and cathode having a second main circuit, and a second control grid for controlling current in the second main circuit, and the second cathode connected to the first cathode; resistance means connected to the cathodes through which the current in both main circuits fiows; an electric generator having a substantially constant field driven at speeds proportional to the speed of the motor; a local output circuit from one output side of the generator, through a local circuit resistor and a capacitor to the other side; a source of potential connected to said one side of the generator; connections communicating potential from said one side of the generator through the local circuit resistor to the said second control grid.

10. In connection with a power system for maintaining a loop in a longitudinally moving strip of material by means of a variable-speed electric-motor provided with means for propelling the strip at one side of the loop; a control system for the motor comprising: a bank of photo-tubes and a source of light, between which th loop is interposed; a photo-tube electric circuit in which current fiows and varies in accordance with changes of light response-oi the phototubes effected by changes of illumination thereof upon shortening and lengthening of the loop; an lectrically energized motor speed controlling circuit; electrically actuated means responsive to a change of photo-tube circuit current occurring upon changing of the loop length and efiective to vary the energization of the speed controlling circuit, to change the speed of the motor; electrically actuated means responsive to said changing of the motor speed and effective only while the motor speed is changing to concurrently oppose the said variation of energization of the speed controlling circuit, to oppose said change of motor speed.

11. A motor speed control system comprising: an electrically energized motor speed controlling circuit; an actuating circuit; means causing actuating current to fiow in the actuating circuit; means responsive to a change of motor speed to change the actuating current; electrically actuated means responsive to a change of actuating current occurring upon a change of motor speed to change the energization of the speed controllingcircuit to tend to restore the motor speed; and electrically actuated means responsive to the changing of the motor speed and effective only while the motor speed is changing to concurrently oppose the change of energization of the speed controlling circuit to oppose restoring of the motor speed.

12. In connection with a power system for maintaining a loop in a longitudinally moving strip of material by means of a variable-speed electric-motor provided with means for propelling the strip at one side of the loop; a control system for the motor comprising: a bank of photo-tubes and a source of light, between which the loop is interposed; a photo-tube electric circuit in which current flows and varies in accordance with changes of light response of the phototubes effected by changes of illumination thereof upon shortening and lengthening of the loop; an electrically energized motor speed controlling circuit; electrically energized controlling means controlling energization of the speed controlling circuit to change the motor speed when a change of the loop length occurs, comprising a first set of electronic tube main electrodes and a circuit thcrethrough in which current fiows controlled in value by a first tube grid, and means to variably energize th grid in response to variations of photo-tube current; and a second means concurrently controlling the energization of the speed controlling circuit tending to prevent said change of motor speed, comprising a second set of electronic tube main electrodes and a circuit therethrough in which current fiows controlled in value by a second tube grid, and means to variably energize the second grid in response to a change of motor speed and directly commen-' surably with the rate of speed change, and efiective only while the motor speed is changing.

13. A motor speed controlling system comprising: an electrically energized motor speed controlling circuit; an actuating circuit; means causing actuating current to flow in the actuating circuit; means responsive to a change of motor -18 4 speed to change the actuating current; controlling means controlling energization of the speed controlling circuit to restore the motor speed responsive to a change of actuating current effected by a change of motor speed, comprising a first set of electronic tube main electrodes and a circuit therethrough in which current flows controlled in value by a first tube grid and circuit means to variably energize the first grid in response to changes of actuating current; another means concurrentl controlling energization of the speed controlling circuit tending to prevent restoring of the motor speed, comprising a second set of electronic tube main electrodes and a circuit therethrough in which current flows controlled in value by a second tube grid; and means to variably energize the second grid in response to said change of motor speed and directly commensurable with the rate of speed change and effective only while the motor speed is changing.

14. In connection with a power system for maintaining a loop in a longitudinally moving strip of material by means of a variable speed motor which moves the strip, a control system for the motor comprising: a source of potential; a first electronic anode-cathode electrode set and a first control grid therefor; a second electronic anode-cathode electrode set, and a second control grid therefor; the anode-cathode sets connected in parallel circuits across the source through resistance means connected to the oathodes, and the cathodes connected together; means responsive to changes of length of the loop to change the energization of the first grid; a control winding in the circuit of the first electrode set energized from the source potential subject to energization of the first grid; means responsive to changes of energization of the control winding to change the motor speed; a constant source of potential energizing the second grid; means producing potential proportional to motor speed; circuit means, effective only while the motor speed and proportional potential are changing, to subject the second grid to potential commensurable .with the proportional potential.

15. In a motor speed controlling system; a source of potential; a first electronic anode-cathode electrode set and a first control grid therefor; a second electronic anode-cathode electrode set, and a second control grid therefor; the anodecathode sets connected in parallel circuits across the source through resistance means connected to the cathodes, and the cathodes connected together; an actuating circuit; means causing actuating current to fiow in the actuating circuit and to vary with variations of motor speed; means responsive to variations of actuating current to vary the energization of the first grid, and means responsive to the consequent variations of current through the first anode-cathode to vary the motor speed; a constant source of potential energizing the second grid; means producing potential proportional to motor speed; circuit means effective only while the motor speed and proportional potential are changing to subject the second grid to potential commensurable with the proportional potential.

16. In connection with a power system for maintaining a loop in a longitudinally moving strip of material by means of a variable speed motor which moves the strip; a control system for the motor comprising: a control winding changes of energization of which changes the motor speed; means responsive to a change of 19 length of the loop to change the tion 0! the winding; means producing potential propor-v tional to the speed of the motor; means actuated by said proportional potential and effective only while. the motor speed is changing, to oppose the change of energlzation oi the winding.

17. In connection with a power system for maintaining a loop in a longitudinally moving strip of material by means of a variable speed motor which moves the strip; a,control system for the motor comprising: control means, responsive to a change of length oi the loop to change the speed of the motor; means producing potential proportional to the speed of the motor; means actuated by said proportional potential and eflective only while it is changing to oppose change or the motor speed by the control means.

18. In connection with a power system for maintaining a loop in a longitudinally moving strip of material by means 0! a variable s means actuated by said proportional potential and effective only while it is changing and directly commensurably with the rate of its changing, to oppose change of the motor speed by the control means.

- WILLIAM FEW.

REFERENCES CITED The following references are of record in the file of this patent:

omen s'ra'rss ra'mn'rs Number Name Date 2,100,715 Jenks Nov. 30, 193'! 2,379,132 Cook June 26, 1945 2,393,015 Bendz Jan. 15, 1948 

